Turbulence compensated throttle control system

ABSTRACT

A system for processing signals representative of airspeed and inertial longitudinal acceleration in first and second channels, respectively, and providing cancellation of the turbulence-induced components of the respective signals. Shear detection and compensation circuits are provided in the system for reducing speed wandering in moderate and heavy turbulence. A circuit processing the signal ΔV from the shear detector circuit is utilized to provide a gust bias signal input in the system.

This invention relates to throttle control systems for aircraft and moreparticularly to throttle control systems including shear detection andcompensation.

Prior art throttle control systems such as shown in U.S. Pat. No.3,840,200 to Lambregts, assigned to The Boeing Company, have providedwindshear detection and compensation; however, the aforementioned systemincluded shear detection and compensation circuits which rejectedinformation herein discovered to be useful in the reduction of speedwandering of the aircraft in moderate and heavy turbulence.

It is accordingly an object of this invention to provide a circuit fordetecting windshear and providing a windshear compensation signal inwhich signal information contained in rejected portions of a limiter inthe circuit is retained and processed in a manner providing reducedaircraft wandering in moderate and heavy turbulence.

It is yet another object of this invention to provide circuit meanscoupled to a shear detector circuit for rectifying the high frequencycontent of the output and filtering the excess above a bias value toprovide a gust bias signal for increasing the speed of the aircraftabove crew selected speed.

Further objects, features, and advantages of the invention will readilybecome apparent from the following specification and from the drawings,in which:

FIG. 1 is a schematic diagram of the system shown in FIG. 5 of U.S. Pat.No. 3,840,200, representative of the prior art; and,

FIG. 2 is a system circuit embodiment of turbulence-compensated throttlecontrol system in accordance with the present invention.

Turning now to FIG. 1 (and FIG. 5 of U.S. Pat. No. 3,840,200corresponding thereto) denoted PRIOR ART, it will be noted that thiscomplete schematic diagram of prior art throttle control systemincluding turbulence compensation utilizes shear detection andcompensation as provided by circuits 58 and 60 to provide the wind shearcorrection signal component. (ΔV). FIGS. 3, 4 and 5, as well as theaccompanying description thereof found in aforereferenced U.S. Pat. No.3,840,200, may be referred to for a clear understanding of the systemand particularly the attendant philosophy involved in the evolution ofshear detection and compensation circuits 58 and 60. It is believed thatsuch will aid in providing a clear understanding and appreciation of howthe signal (ΔV) output from washout and lag circuit 58 is generated andtherefore how it can be utilized at lead 701 (as seen in FIG. 2) andprocessed to provide gust bias signal 729 as hereinafter described. Suchan understanding will further facilitate comparison and appreciation ofthe features and advantages of circuit 600 of FIG. 2 when compared tothose of rate limited lag circuit 60 of FIG. 1.

Briefly, considerations in the design of the shear detector circuithaving low sensitivity to turbulence comprising circuits 58 (of FIGS. 1and 2,) and 60 (of FIG. 1) for providing the correction term ΔV to besubstracted from V_(b) are now noted. In this connection a singlecomplementary washout and lag type filter having a time constant of 10seconds provided adequate windshear performance. This allows ΔV to bebuilt up with a rate of 0.1 knot per second² for a step input of 1 knotper second. The rate limit for limiter circuit 50 in the rate limitedlag circuit 60 (of FIG. 1) may therefore be set at 0.1 knot per second²for a loop gain K₅ of 0.1. A further consideration affects the selctionof the values of gains K₄, K₅, of amplifier circuit means 46 and 52respectively and the rate limit of limiter circuit 50 in the system ofFIG. 1. The smaller the rate limit selected, and the higher gain valueK₄ that is chosen, the higher percentage of time the rate limit circuit50 will be saturated by turbulence, thus preventing the development bycircuits 58 and 60 of a signal ΔV to be subtracted from the signalΔV_(b) to provide a signal V representative of longitudinal accelerationwhich is corrected for windshear. Shear detection and compensation asprovided by circuits 58 and 60 coupled between the V_(E) signal channeland the V_(b) signal channels would in such a case be adversely affectedby the level of turbulence. This is minimized in the system design ofFIG. 1 by selecting K₄ =5, K₅ =0.2 knots per second². These valuessufficiently suppress turbulence response of the shear detector circuitand do not deteriorate the turbulence immunity of the autothrottlecontrol system. The shear detector utilizes as an input, the air speederror signal V_(E) without effecting autothrottle system performance forstep changes in air speed. For a step introduction of a 1.0 knot persecond windshear in smooth air, the peak value of air speed errorremains limited to about 4 knots.

In FIGS. 1 and 2 a further advantageous feature of the rate command typeautothrottle systems should be noted in the mode of operation occurringwhen either the forward or aft throttle limit position is reached. Wheneither of these two autothrottle conditions is detected by the closingof one of throttle limit switches 70 or 72, autothrottle limit logiccircuit 74 generates at the output thereof a servo loop disengage signalcausing switching means 76 to close a signal path includingsynchronizing amplifier 78 from the output of adder 26 back to the inputof adder 19, thereby synchronizing the total servo command input toservo means 10 to zero. The autothrottle control systems are reengagedsubsequently when the sum K₁ V_(E) +K₂ V changes sign (polarity fromzero). Sign detector circuit 80 or 82 detect the positive or negativepolarity change respectively of this sum as provided at the output ofadder circuit 18. This circuitry to provide anticipation of throttlecommand to drive the throttle out of the limit position is thereforeproportional to V, as required to provide capture of the selected speedV_(SEL) asymptotically. The total servo position error, (δT_(CMD) ΔδT)is synchronized to zero when switching circuit 76 is in the disengagedposition to insure that the servo 10 comes out of the limit positionwithout a step transient. Such a step transient could occur due to thepresence of the position command signal proportional to accelerationcoupled through amplifier 28 and present as an input to adder 26, ifthis signal was not zeroed by the synchronization loop. Switching means76 is driven to the engage position when the output of AND circuit 92 ishigh, which requires that the system engage switch 90 is engaged andboth outputs of circuit 301 and 300 are high.

The output of circuit 300 is normally high except when circuit 70 ishigh, signifying that the forward throttle limit is reached and circuit82 is low, further signifying that there is no command to drive thethrottles aft, so that in this case both inputs to circuit 300 are highand the output of circuit 300 is low. The output of circuit 301 isnormally high except when circuit 72 is high, signifying that the aftthrottle limit is reached and circuit 80 is low, further signifying thatthere is no command to drive forward, so that in this case both input tocircuit 301 is high and the output of circuit 301 is low.

The gain value for K sync amplifier 78 determines how fast the positionerror is nulled out. For a gain factor of 10 the position error goes tozero in less than 1 second.

The feedback loop for the position servo 10 comprises tachometer means84 coupled from the output of servo 10 back to an input of adder circuit19. If the servo motor 10 rotates at a given rate, then the throttleposition δ_(T) is a ramp function. Mathematically the change in throttleposition Δδ_(T) is the integration of the servo or throttle rate, that,Δδ_(T) =δ_(T) /S. The tachometer 84 is actually a generator whichproduces a signal proportional to the angular velocity of the motor 10or proportional to the differentiated throttle position that is δ_(T)=Sδ_(T). Throttle position as the feedback signal is obtained using thetachometer signal K_(T) Sδ_(T) =K_(T) δ_(T), which is then integrated incircuit 16 yielding K_(T) /Sδ_(T) =K_(T) Δδ_(T), thereby providing anoutput signal proportional to the actual position change Δδ_(T) utilizedto cancel the throttle position command signal Δδ_(T) CMD at addercircuit 26. The servo 10 therefore sees a signal outputted from adder 26which is proportional to the difference of throttle position commandprovided in the systems of FIGS. 1 and 2 in accordance with theautothrottle control law of these systems and the signal representativeof actual throttle position change Δδ_(T) . The throttle servo motor 10will therefore run with an angular velocity proportional to the positionerror of the throttle 94 and come to a stop only when true positionerror has reached zero.

The servo motor 10 drives the throttle means 94 through a clutch means96 which is normally engaged. The throttle levers indicative of throttleposition 98 control the amount of fuel passing to engine 99. When thepilot applies a force to the throttle levers denoted Δδ_(T) pilot,clutch means 96 disengages so that the throttle servo 10 no longerdrives the levers. This allows the pilot to take over throttle controlat any time.

As hereinbefore mentioned, the improved system of FIG. 2 includes sheardetection and compensation circuits 58 and 600 which provide thewindshear compensation signal ΔV. In shear detection circuit 58 of FIG.2 it should be noted that the second input to combining circuit 44comprises a signal representative of airspeed rather than airspeederror, as in the circuit 58 of the system of FIG. 1. In compensationcircuit 60 of the system of FIG. 1, limiter circuit 50 rejected signalinformation exceeding the limits, thereby causing speed wandering inmoderate and heavy turbulence, the wandering being directly related tothe asymmetry between positive and negative peaks of the signal outsidethe limits. Compensation circuit 600 in contrast retains signalinformation over the limit (signal 631 minus signal 636) providingamplification thereof with a gain K₇ in amplifier circuit means 616 andsubsequent integration in integrator circuit 618 as limited signal 633is also similarly processed with a gain K₅ in amplifier circuit means606 and subsequently integrated in integrator circuit 608. The path forsignal 640 with a low gain K₆ through amplifier circuit means 614 tocombining circuit means 612 provides equalizing with no dynamicsignificance. Signal path splitting is thus seen in circuit 600 whereinthe signal within the limits of limiter circuit 604 is filtered slightlyfor rapid system response, whereas the signal path outside the limitsprovides heavier filtering for noise rejection.

In moderate or heavy turbulence signal 643 is very noisy and isattentuated by low pass filter circuit 620 prior to being added assignal 627 in combining circuit 610 to provide signal 623 representativeof ΔV.

More specifically, in the present turbulence-compensated throttlecontrol system of FIG. 2 shear detection and compensation are providedby washout and lag circuit 58 and compensation circuit 600 where inputsignal 621 representative of ΔV which is provided at output terminal 601of washout and lag circuit 58 is coupled to a first input of firstcombining circuit 602. The output signal 628 at output terminal 632 ofcombining circuit 602 is coupled through a first signal path 629 tolimiter circuit 604 and through a further signal path 636 to a firstinput of second combining circuit 612. Output signal 633 from limitercircuit 604 is coupled through signal path 631 as a second input tosecond combining circuit 612 and also through signal path 635 toamplifier circuit 606. The output of amplifier circuit 606 is coupledthrough signal path 638 to integrator circuit 608, the output path 639of integrator circuit 608 being coupled through terminal 641 to providea first input signal 626 to third combining circuit 610. Signal path 640coupled from terminal 641 through amplifier circuit 614 provides a thirdinput to second combining circuit 612 and the hereinbefore discussedequalizing path in the particular type signal processing provided bycircuit 600. Output signal path 636 from second combining circuit 612 isconnected in series circuit path through amplifier circuit 616 andintegrator circuit 618 to common terminal 644, common terminal 644 beingconnected to a third input terminal of first combining circuit 602 andfurther connected to low pass filter circuit 620 for providing signal627 containing useful data information outside the limits of limiter 604as a second input to third combining circuit 627. Output signal 623(representative of ΔV) from third combining circuit 610 is coupled to aninput of combining circuit 56 in the system of FIG. 2 to provide theshearcorrected signal as was the signal ΔV in the system of FIG. 1.

A further feature hereinbefore referred to in the system of FIG. 2comprises the circuit path coupled between output terminal 601 ofwashout and lag circuit 58 and an input of adder circuit 18 forproviding gust bias signal 729 to increase speed with increasing levelof turbulence. The signal ΔV representative of air mass motion withrespect to the ground varies rapidly in turbulence and is coupled fromoutput terminal 601 through high pass filter 703 to rectifier 705 sothat the high frequency components of the aforesaid signal are rectifiedand subsequently coupled through combining circuit 711 so that valuesexceeding bias level 709 are provided at terminal 713 and a first inputterminal of combining circuit 715 and appear as input signals 721 to lowpass filter and limiter circuit 723 having limits of zero and about tenknots, thereby limiting the amount of "fly fast" command imparted atcombining circuit 18 of the throttle control system of FIG. 2. Signaloutput 725 from low pass filter and limiter circuit 723 is then coupledthrough amplifier circuit 727 to an input of adder circuit 18. Normallyopen switching means 717 connected between terminal 713 and circuit path719 to a second input of combining circuit 715 is closed upon extensionof landing flaps in landing configuration of the aircraft, therebycausing a doubling in amplitude of gust bias signal 729 for providing anincreased speed margin in the case of turbulence during landing.

We claim:
 1. In combination in an autothrottle control system for anaircraft;means including a first signal control channel for processing asignal representative of airspeed error and providing an output; meansincluding a second signal control channel for processing a signalrepresentative of inertial longitudinal acceleration and providing anoutput; means for combining the outputs of said first and second signalcontrol channels to provide a throttle command signal; means forproviding a signal representative of airspeed; washout and lag circuitmeans having an output, said washout and lag circuit means coupledbetween said second signal control channel and said means for providinga signal representative of airspeed; a signal processing circuitconnected in series circuit path between the output of said washout andlag circuit means and said second signal control channel, said signalprocessing circuit including a limiter circuit (604) and subtractionmeans (612) for subtracting the limited signal (631) from the inputsignal upstream from said limiter circuit to provide a remainder signal(636), said signal processing circuit further including a filter circuit(620) for processing said remainder signal and combining circuit means(610) for adding an integrated limited signal (626) and the processedremainder signal (627); and, gust bias signal generating means coupledbetween said output of said washout and lag circuit means and said firstsignal control channel.